Various methods are known by which a belt (including a tube, hereafter referred to as belt) is produced with a resin. For example, a resin solution having a heat-resistant resin or a resin source material dispersed or dissolved in a solvent is applied onto an outer surface of a cylindrical or tubular surface-treated mold or applied onto an inner surface of a tubular mold and, after thickness adjustment, evaporating the solvent by heating or evaporating the solvent by preheating, and then heat-curing it to produce a belt.
In evaporating the solvent by heating, the heating must be carried out moderately at a temperature lower than thereby raising a problem that repellency of the solution occurs and pinhole defects are liable to occur. For this reason, the yield of the products has not been high.
One method for fabricating an endless belt is a method by extrusion. By this production method, an endless belt is obtained by extruding a thermoplastic resin in a hollow state and cutting it to a suitable length. This method is a fairly effective method as a method for obtaining a long product having a wide belt width. However, by this method, it has been extremely difficult to mold a thin resin belt. Also, there is a limit to the dimension precision, so that at most about 5 to 10% of the thickness of the molded product is near the limit, and actually there has been a variation more than that. Moreover, it has a disadvantage that the apparatus will be considerably large and expensive in order to obtain a belt having a large diameter by this production method.
A still another method for obtaining an endless belt is a method by injection molding. This molding method involves molding by injecting a thermoplastic resin into a mold and is advantageous in that a product having a desired shape and size can be obtained. Further, this method is a useful method because a three-dimensional complex shape is also obtained. However, by this method, the mold will the boiling point of the solvent in order to suppress foaming from the inside of the resin, and it is not preferable to perform the heating at a temperature which is too high. Further, in order to prevent the solvent from remaining in the obtained belt, this drying step requires a period of time at least in minutes, specifically in five to ten minutes, and if it is possible in production, it is preferable to perform the drying step for a longer period of time in view of the characteristics of the product. Further, the heat-curing requires a considerable period of time depending on the type of the resin, and it requires at least four to five minutes or, if it is long, thirty to forty minutes, and an even longer period of time is required in order to raise the curing degree.
Due to such a low productivity, a large amount of expensive mold and a wide production space are needed in the case of manufacturing a large amount of products. Also, by this method, the fabricated resin belt may be brought into close contact with the mold as if being bonded thereto, making it difficult to peel the belt from the mold. In this case, the expensive mold must be protected at the cost of the product, thereby all the more aggravating the productivity. Further, in order to facilitate lubrication, the mold must be subjected to a lubrication treatment, be expensive and the apparatus itself will be large and expensive in order to mold a large-size one. Further, concerning the precision of the molded product, the dimension precision of the thickness has a limit of about 0.05 mm besides the size of the outer diameter, so that it cannot be said to be a good one. Further, it cannot be said to be a preferable method for molding a product having a small thickness.
On the other hand, as a method for obtaining a belt, there is a method in which a resin film is produced in advance and the ends of the film are bonded. In this method, a thermoplastic resin is used for bonding the seams, or the belt itself is formed of a thermoplastic resin and the seams are superposed one on the other and thermally welded; however, there has been a problem such as brittleness of the physical strength of the seams and the difficulty of forming it into a plane.
Furthermore, in an electronic photography apparatus such as a copier, a method is known in which paper is conveyed by mounting the paper on a resin belt such as PC or vinylidene fluoride, or in which the resin belt is electrically charged in advance to impart an electric charge to the surface thereof and the paper is conveyed by allowing the paper to be adsorbed by the electric charge. In the method of conveying the paper by mounting it on the resin belt, the paper and the belt often slip with each other and it is difficult to realize a stable transportation. On the other hand, the method of allowing the resin belt to be electrically charged for allowing the paper to be adsorbed has a problem such that the adsorption force of the paper is insufficient and it is not possible to fix the paper on the belt with good precision, and moreover the tip end of the paper floats up during the transportation. In particular, in order to achieve high speed of a printer, it has been necessary to allow a printing medium such as paper or OHP film to be adsorbed onto the belt with good precision, and to raise its adsorption power. Furthermore, it has been necessary to ensure a sufficient power of adsorbing the paper even if the environment of use changes, e.g., even under a high-temperature and high-humidity. For this reason, in order to achieve a high speed of a printer or the like, there is a medium conveying belt capable of strongly adsorbing a medium such as for printing adopts a method in which an electrode pattern is formed on a belt and applied a voltage thereof so that the paper is electrostatically adsorbed.
Conventional conveying belts have been extremely expensive because they are originally expensive and also a special apparatus or means is used in order to form an electrode by further processing them. Regarding the conventional conveying belts, a seamless belt (hereafter referred to as endless belt) is produced by a method such as described above, and the obtained endless belt is further processed to form an electrode pattern having electrical conductivity; however this leads to processing an expensive endless belt further with an expensive apparatus. For example, the electrode pattern having electrical conductivity is formed by performing printing, vacuum deposition, etching, plating, or the like; however, it is a considerably difficult work to perform such a processing on an endless belt. Though screen printing on a plane is easy, printing an electrically conductive paste on a tubular object by curved-surface printing requires a special apparatus, leading to poor yield and increased costs.
Further, in recent years, there is a tendency that electrophotographic devices, ink jet printers, or bubble jet printers are becoming smaller and less expensive. For this reason, the medium conveying belt used in these devices require compact designs. In particular, if an electrode is exposed for applying a voltage to the surface on which the medium is conveyed, it will be an obstacle in reducing the scale of the device. This is because it requires an area for exposing the electrode in addition to the area for the objects to be adsorbed, and moreover the presence of a power supplying brush restricts the freedom of the site for printing characters or transcribing images on the medium, thereby all the more increasing the size of the device. Therefore, a medium conveying belt has been demanded which has a construction such that an electrode protective layer is further provided on the electrode pattern. However, in addition to the difficulty in forming an electrode pattern after fabricating a tubular object in view of forming the electrode pattern on a curved surface, there is a problem of increase in costs because since the device must undergo a complicated process of attaching an electrode pattern on a curved surface after manufacturing a tubular object and thereafter forming an electrode protective layer.
Thus, as a result of repeated eager studies and development in order to obtain a manufacturing method by which an endless belt having an arbitrary size and thickness can be mass-produced stably and inexpensively and moreover the characteristics of the belt can be suitably adjusted, the inventors of the present invention have arrived at a concept of the multi-layered endless belt of the present invention and its manufacturing method, and further arrived at a concept of various medium-conveying belts using the same, their manufacturing methods, and apparatus for forming the same.